When I first started shooting muzzleloaders, back in the '80s, Forster used to sell a gadget called a "Tap-A-Cap" You used it along with a mallet to turn aluminum beer can material into percussion caps. The priming explosive was two or three dots from toy caps inserted inside these cups. Too bad it's been discontinued.

I actually experimented with plastic toy caps on percussion guns but the explosive mixture in these was not powerful enough for consistant ignition, in fact for every successful firing, there were several unsucessful pops with no boom, even with my Ruger Old Army with its fairly large flash holes and direct path to the chambers.
If I can't get more caps within a year or so, I might revisit that experiment but this time fortify the explosive material with extra dots from toy paper caps.

I have also heard of people succesfully using the white tips of strike anywhere kitchen matches as priming explosives.

I honestly never thought this buying panic would affect .22 rimfire and percussion caps when it started. Roundballs, muzzleloading bullets, and Pyrodex/777/BH-209 are all in stock at my local retailer along with some centerfire ammo but percussion caps and .22 rimfire ammo is unobtainium right now.
Bullets for reloading .22 centerfire are starting to show up on the shelves again, cause for hope.
Really, I think this too will pass.